1. Field of the Invention
This invention pertains to oscillators generally, and more specifically to housings or packages for temperature-controlled crystal oscillators that are simultaneously compact, rugged, and amenable to mass-production techniques.
2. Description of the Related Art
In a TCXO, electronic circuitry necessary to provide basic electrical oscillation and temperature compensation will most desirably be placed as close to the crystal as possible, since the temperature being measured will desirably be that of the crystal. The electronic circuit should also be close, owing to the high frequencies of oscillation which are adversely affected by long lead lengths. This has been accomplished in the prior art by including the electronic circuitry adjacent to the crystal, such as illustrated by Shigemori et al in U.S. Pat. No. 6,081,164. Unfortunately, the discrete package which is provided as important physical isolation for the crystal adds volume to the second package, making the finished oscillator quite large. Consequently, this design has not been widely accepted in the handheld marketplace.
Several additional designs, which are commonly owned by the present assignee, have been proposed that have proven to be successful in the marketplace. U.S. Pat. No. 5,438,219 to Kotzan and Knecht, and U.S. Pat. No. 5,500,628 to Knecht, the contents which are incorporated herein by reference for teachings found therein, each illustrate packages which accommodate oscillator and temperature control circuitry within a package which also separately houses a crystal resonator. The novel oscillator packages illustrated therein enabled the manufacture of a reliable package of smaller dimension than was previously possible, reducing the package size from 8.89 mmxc3x978.89 mmxc3x972.79 mm down to 7.11 mmxc3x976.22 mmxc3x972.24 mm. While those dimensions are already quite small, the demand continues for even smaller and lower cost components. Unfortunately, these patents also require that electrical connections be made within a package cavity. This eliminates the use of low-cost screened and re-flowed solder attachment, which is very amenable to high volume production, and instead requires alternatives such as wire-bonding to be used in a greater degree.
In a first manifestation, the invention is a temperature compensated oscillator assembled on a crystal package base. A planar substrate has first and second major surfaces forming opposite sides of the crystal package base. Sidewalls adjacent the first major surface extend upwardly therefrom and form a cavity therewith. The cavity is adapted to receive at least one piezoelectric component, and the second major surface is adapted to receive at least one electronic component. A cover is coupled to the cavity and defines a hermetic enclosure therewith. An encapsulant and the second major surface encapsulate the electronic component.
In a second manifestation, the invention is a method of coupling components to a crystal package. A ceramic package having an open receptacle with a planar exterior is provided. A piezoelectric element is mounted in the open receptacle. The piezoelectric element is frequency tuned, and then hermetically sealed in the open receptacle. Electronic components are affixed to the planar exterior and electrically coupled to the piezoelectric element.
In a third manifestation, the invention is a method for assembling a temperature compensated crystal oscillator. In this method, the steps are: providing a double-sided TCXO package body with a first planar surface and a cavity opposite the first surface; attaching compliant crystal supports into the cavity; placing a piezoelectric device into the crystal supports; hermetically sealing the cavity with a cover, applying a conductive composition onto the first planar surface; positioning electrical components into the conductive composition; affixing and electrically connecting the electrical components to the conductive composition; dispensing encapsulant substantially over the electrical components; and curing the encapsulant to yield an assembled TCXO.
Exemplary embodiments of the present invention solve the inadequacies of prior temperature compensated crystal oscillator circuits by providing a three-layer ceramic package with a crystal sealed in a well or cavity. Oscillator components are attached through screened solder onto the back side of the ceramic package and are encapsulated within potting compound or encapsulant.
A first object of the invention is to enable low-cost mass-production manufacturing techniques, while still ensuring the integrity of sensitive and critical parts within the oscillator. A second object of the invention is to provide a temperature compensated crystal oscillator (or other type of oscillator circuit) with output frequency that deviates less than +/xe2x88x922 parts per million (ppm) over a temperature range of xe2x88x9230xc2x0 to +85xc2x0 C. Another object of the present invention is to provide a temperature compensated crystal oscillator with an output frequency that deviates less then approximately +/xe2x88x921 ppm over a one-year aging period. A further object of the invention is to minimize the possibility of cross-contamination of the components by isolating the crystal from other components. Yet another object of the present invention is to provide a temperature compensated oscillator that may be packaged into a smaller package than was heretofore possible.